1. Field of the Invention
The present invention generally relates to ETSOI MOSFETS, and more specifically to robust isolation for ETSOI MOSFETS.
2. Description of Related Art
Metal Oxide Semiconductor Field Effect Transistors (MOSFETS) are commonly used today in almost all electronic circuit applications. An emerging technology in the field of semiconductor-on-insulator (SOI) FET devices is the extremely thin semiconductor-on-insulator (ETSOI) MOSFET. Such a device shows excellent short channel control, which is desirable. With the trend toward continued scaling of MOSFET devices, ETSOI is a promising candidate for next generation technology.
There are, however, several manufacturing issues that can limit yield. Specifically, as the STI divot erodes as a function of the HF based cleaning and other process steps during manufacturing, the back gate or substrate wafer is exposed, leaving it susceptible to shorting due to source/drain epitaxial growth and unwanted metal gate connections, among other processes.
Referring now to FIG. 1A, a problem inherent in some current ETSOI devices is illustrated. FIG. 1A illustrates a wafer including a substrate 102, a buried oxide layer 104 and an ETSOI layer 106. It also includes raised source/drain regions overlying the ETSOI layer 106 and adjacent to the gate structures 108. Also shown is a dielectric 110 within the illustrated shallow trench isolation region. During normal processing, epitaxially grown silicon can develop along the sidewall of the shallow trench isolation region. In FIG. 1A, this is illustrated as epitaxially grown silicon 114. As illustrated in FIG. 1A, epitaxially grown silicon 114 forms an unwanted connection from the substrate 102 to the raised source/drain region 112.
Referring now to FIG. 1B, another problem inherent in some current ETSOI devices is illustrated. FIG. 1B illustrates the device after the deposition of a pre-metal dielectric 116 and the formation of contact holes. In the case of a mis-aligned contact hole 118, the hole can be etched partially into the shallow trench. This presents a problem when metal is later added, as it can also create a short between the substrate 102 and a raised source/drain region